Heavy hydrocarbons such as paraffins and asphaltenes are commonly found in a wide variety of crude oil from many different areas, from field to field in the same area and indeed in certain cases from well to well in the same field.
Asphaltenes are large aromatic agglomerates composed primarily of heterocyclic rings which are normally held in solution/suspension in crude oil by naturally occurring, petroleum resins that adhere to the outer surface of the asphaltene agglomerate. However, it is well known that they can precipitate and deposit in production lines, transfer lines, storage tanks etc particularly where pressure drops allow the resins to desorb.
Paraffins on the other hand are saturated hydrocarbon waxes that precipitate and deposit in areas where decreases in temperature below the solubility temperature of the paraffins in the crude oils results in the appearance of wax. This is commonly known as the wax apparent temperature (WAT). Asphaltenes and paraffins have the common characteristics that they can inhibit or block production from the well, foul transportation lines and form unwanted deposits in storage tanks.
Because of their differences in character, the control of asphaltenes may not necessarily result in the control of paraffins and vice versa. Accordingly crude oil is tested to determine paraffin/asphaltene content to determine what form of treatment best suits the particular crude oil. Complicating the problem is that in most crude oils both asphaltenes and paraffins are found albeit that one may be present in a much larger amount then the other.
The problem of heavy hydrocarbon control i.e. paraffin and asphaltene control, involves two main approaches (1) removing already formed deposits where they are causing a problem and (2) minimizing the formation of deposits. As is well understood by those in the art because of the complexity of the problem there is generally not one solution to controlling asphaltene problems and paraffin problems.
With respect to existing deposits, in the case of paraffins, as noted above, even slight changes in an equilibrium condition involving the solution of the paraffin waxes in crude oil can cause precipitation of the paraffin wax. One such change of an equilibrium condition can be reduced temperatures.
In the case of paraffins, it is known that particulate matter in the crude oil speeds precipitation of the wax since such particulates act as a nucleus for the formation of large paraffin particles from smaller particles suspended in the crude oil. It is these larger particles which, under certain conditions will precipitate forming the problems discussed above.
In the case of asphaltene deposits, asphaltenes and other heavy hydrocarbon materials such as asphaltenes are frequently found as suspended solid particles in the crude oil. These heavy asphaltene type molecules often occur in colloidally suspended solid particles which fall out of the crude oil e.g. precipitate, where conditions that kept them dispersed changed. Many of the same factors affecting the buildup of paraffin wax and its precipitation are the same factors which will lead to the precipitation of asphaltenes and similar heavy hydrocarbons from the crude oil. It is also known that asphaltenes and the problems caused thereby generally occur in the well adjacent producing formations, which is generally not the case with paraffin wax formation.
A commonly used solvent, BETX (benzene, ethylbenzene, toluene, and xylene), has been used and is effective at removing paraffins deposits but is encountering increasing resistance to use due to environmental concerns, governmental regulations, particularly on offshore applications, and relatively low flashpoint which poses further safety problems during transport and handling.